National Electrical Installation Standards

Standards as High as Your Own

?
Thursday, May 18, 2017

Question:

Charlie, Thanks for your work on this important public service.

When feeder or branch circuit conductors are run in parallel, does the EGC ever have to be larger than the ungrounded conductors?  The folks that wrote the code handbook seem to think so, BUT the last sentence of .122(F) states "Each equipment grounding conductor shall be sized in compliance with 250.122."  That takes you to 250.122(A) first sentence that states"shall not be smaller than shown in Table 250.122".... but that sentence has a commma and we need to keep reading to the end. Immediately following the mandatory use of the column is the statement "but in no case shall they be required to be larger than the circuit conductors supplying the equipment."  It is in the same sentence.

I think "in no case" means just that, in no case will the table drive you to size an equipment grounding conductor larger than the circuit conductors.  Including the case of the parallel conductors.

If you go back to the more clear wording of 250-95 in previous versions of the code ( I went to the 1993), back before the removal of exceptions was made for "clarity and usability" the intent is much more clear.  Exception 2 has the wording that is now permissive language in .122(A) and exception 2 to 250-95 applies to the parallel conductor statement.

Thanks for giving us your take on this issue.

Greg McMurphy

A

Answer:

Hey Greg thanks for your question and you are welcome. This is often a point of confusion. The circuit conductors in a parallel arrangement include all the conductors that make up each phase or grounded conductor. The conductors connected in parallel are added together to determine the equivalent size. So if there were two 500 kcmil conductors in parallel for each phase the area of each phase is 1000 kcmil. Equipment grounding conductors in a raceway that is part of a parallel arrangement might need to be larger than the ungrounded conductors in that raceway but will not need to be larger than all of the ungrounded conductors of any given phase - even in the 1993 NEC.

ABOUT CQD: NECA’s Code Question of the Day (CQD) is a leading National Electrical Code® forum for NECA and the industry. The CQD generates a lively dialogue and relative practical and Code-based responses to an ever-increasing and interactive audience.

IMPORTANT NOTICE: All answers are based on the latest edition of the National Electrical Code®, unless the question requests a response based on a specific edition. This correspondence is not a formal interpretation of the NEC®. Any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, or any technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.

ABOUT CHARLIE: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Charlie was also a member of NECA’s Academy of Electrical Contracting. Charlie’s experienced team of industry experts keep the CQD dialogue and discussions active and informative in the spirit of the man himself, as he wanted.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. Visit NECA-NEIS.org for more information. NEISÔ can be purchased in three formats: as paper books, on CD, or as electronic downloads.

NECA SAFETY PRODUCTS: NECA publishes valuable electrical safety books and CDs for the industry. Visit necanet.org/store to view or purchase NECA safety products.

 CONTACT US: To submit a Code question, subscribe, or unsubscribe from this list, please e-mail: codequestion@necanet.org.